Circuit interrupters



1957 w. D. KYLE, JR.. ET AL 2,804,520

CIRCUIT INTERRUPTERS 4 Sheets-Sheet 1 Original Filed Aug. '21., 1950 RNA R w H 5 OER N T m KV W mum n n M m mm M N LT lllflfl lnn m w m T m m Wa l w Y m B lNsuLATu OIL LEVEL Aug. 27, 1957 w. D. KYLE, JR, ET AL 2,

. CIRCUIT INTERRUPTERS Original Filed Aug. 21, 1950 4 Sheets-Sheet 2 II"I--' I= I I. 4 43 3 26 lo IO lnsuLm' ou i 25 l5 '5 22- INSULATI |4 l7I? i 20 I3 9 M 3 9 23 INVENTOR WILLIAM D. KVLE,JR.

BY ANTHONY VAN RYAN A T TOR NEY Aug. 27, 1957 w. o. KYLE, JR. ETAL 2,

CIRCUIT INTERRUPTERS Original Filed Aug. 21. 1950 4 Sheets-Sheet 3lHSULATlON b5 INVENTOR cmwlffciggfirg WILLIAM D. KYLE, JR

R 66 BY ANTHONY VAN RYAN ATTORNEY Aug. 27, 1957 w. D. KYLE, JR. ET AL2,304,520

CIRCUIT INTERRUPTERS Original Filed Aug. 21. 1950 4 Sheets-Sheet 4Jiilorny United States Patent CIRCUIT INTERRUPTERS William 1). Kyle,.lr., Milwaukee, Wis., and Anthony van Ryan, Ocean Springs, Miss.,assignors to McGraw- Edison Company, a corporation of DelawareContinuation of application Serial No. 180,580, August 21, 1950. Thisapplication February 24, 1955, Serial No. 490,359

4 Claims. (Cl. 200-89) This invention relates to circuit interrupters.

This application is a continuation of our prior application, nowabandoned, Serial No. 180,580, filed August 21, 1950, for CircuitInterrupters, which latter is a continuation-in-part of our applicationSerial No. 665,048, filed April 26, 1946, for Circuit Interrupters, andnow abandoned.

Objects of this invention are to provide a circuit interrupter which isso constructed that it will open the circuit after an overload only whenthere is no current flowing, the circuit interrupter being designed tobe used in cooperation with a reclosing circuit interrupter, thereclosing circuit interrupter being placed in the main line and thecircuit interrupter forming the subject of this invention being placedin a branch line or a continuation of the main line.

In greater detail, further objects are to provide a circuit interrupterwhich may be called a counting, single shot circuit interrupter whichhas a counting means for tripping the circuit interrupter, in which thecounting means is advanced towards tripping position in a step-by-stepmanner upon cessation of current following overloads, and in which thecounting means is finally moved to a position to trip the circuitinterrupter when there is no current flowing following the occurrence ofthe last overload of the series for which the device is adjusted.

Further objects are to provide a circuit interrupter of the characterabove set forth in which adjustable means are provided for adjusting orsetting the device so that trip out of the circuit interrupter during acurrent zero will occur after any given number of overloads for whichthe interrupter is adjusted, provided the overloads recur in asufficiently rapid sequence, means being provided whereby a gradualresetting of the count-ing means takes place either after trip out ofthe circuit interrupter or when there has been a lesser number ofoverloads than that for which the device is set, or when such overloadsoccur at widely spaced intervals.

Further objects are to provide a circuit interrupter in which thecounting means which trips the circuit interrupter is operated bycurrent responsive means when the current responsive means is returningto its initial position and which is not operated by the currentresponsive means when the current responsive means is being moved due toan overload, the construction thereby guarding against any violent shockto the counting means on heavy overload.

Further objects are to provide a circuit interrupter in which thecounting means is not operated by pawl and ratchet mechanism withassociated mechanical escapement mechanism for final return of thecounting means to its initial position, but in which the counting meansis actuated hydraulically by current responsive pumping means, thepumping action occurring on cessation of current fiow, provision beingmade for the gradual discharge of liquid from the counting means toprovide for the final return of the counting means to its initialposition.

"ice

It has been found that where a magnetic pumping plunger is employed inan alternating current circuit interrupter, that it frequently happensthat the minute vibrations of the pumping plunger due to the alternatingcurrent will cause an undesirable pumping of oil. This is particularlytrue as minimum trip value of current is approached.

This invention is designed to overcome the immediately above statedobjections and a further object of this inventionis to so construct themagnetic plunger and its associated valve structure that theircorrelation prevents undesirable pumping of oil and only allows pumpingof oil at the desired time for proper functioning of the circuitinterrupter.

Embodiments of the invention are shown in the accompanying drawings, inwhich:

Figure 1 is a vertical sectional view partly broken away through thecircuit interrupter.

Figure 2 is a sectional view on the line 22 of Figure 1.

Figure 3 is a fragmentary sectional detail of a further form of theinvention.

Figure 4 is a view showing the distribution system in.

which the circuit interrupter is used.

Figure 5 is a fragmentary sectional detail view showing a further way inwhich the device may be constructed.

Figure 6 is a fragmentary sectional view of the intake valve of Figure5.

Figure 7 is a side elevation, partly in section, of the impulse valve ofFigure 5 showing such valve removed from the remainder of the apparatus.

Figure 8 is a bottom view of the impulse valve.

Referring to the drawings, it will be seen that the circuit interrupteris mounted within a tank or can 1 having closed bottom and side wallsterminating in a beaded upper edge indicated at 2. The tank is closed bymeans of a top or cover 3 which has a gasket 4 resting upon the beadededge 2 of the lower portion of the tank. The tank is provided with abracket 5 of any suitable type, whereby it may be attached to a pole orother support in the usual manner. The top is held to the tank by anysuitable means, as by means of the bolts 6 and nuts 7. Insulatingbushings 8 extend downwardly into thhe tank and below the oil level asindicated and carry terminals, not shown, at their upper ends inaccordance with the usual practice. The tank is preferably lined with afiber lining 9.

The entire circuit interrupter is supported from the cover 3. Insulatingtubular members 10, attached to the cover in any suitable manner, extenddownwardly and receive the bolts 11 by means of which the insulatingportion 12 of the contact assembly is held in place. This insulatedsection may take any suitable form. It is preferably provided with sidewalls 13 between which the movable and stationary contacts arepositioned. The stationary contacts are indicated by the referencecharacter 14 and the movable contacts by the reference character 15. Themovable contacts are carried by metal arms or levers 16 which arepivoted at 17 and are provided with metal spacers 18 against which theends of a U-shaped bronze or other metal conducting member 119 bears.The inner ends of the arms 16 are slotted as indicated at 20 and receivethe pin 21 carried by the insulating slide rod 22. When the switch is inclosed position, the parts are as shown in Figure 2. In order to openthe switch, the slide rod 22 is pulled upwardly by means hereinafterdescribed and suddenly separates the movable contacts from thestationary contacts and rocks the levers or arms 16 downwardly intocontact with the insulating bushings or spacers 23 for the lower portionof the side walls 13,

and thus limits the upward travel of the slide rod 22 as well as thedownward rocking motion of the movable contacts 15. A pair of tensionsprings 24 are connected to a transverse pin 25 at their lower ends andat their upper ends are anchored to the top 3 of the casing. Thesesprings, therefore, constantly pull upwardly on the slide rod 22. Thepin 25 serves to pivot the lower arm 26 of a toggle link mechanism, theupper arm of such toggle link mechanism being indicated at 27, the armsbeing pivotally joined together as indicated at 28. In reality, the arm26 consists of a pair of links as shown most clearly in Figure 2 locatedon opposite sides of the slide bar 22. A small latch 29 is pivotallycarried by the lower arm or arms 26 of the toggle link and normallylatches a downwardly projecting extension 30 of the upper arm 27 of thetoggle link mechanism. The latch 29 is spring urged as indicated at 31in a counter-clockwise direction and is provided with an extension ortrip engaging portion 32. The upper end of the arm 27 rigidly carries apin 33 which is pivotally mounted in one of the arms 34 of a bell cranklever, the other arm of such bell crank lever being indicated by thereference character 35.

It is to be noted that the pin 33 is diametrically cutaway at one endand the remaining half of the pin bears against a shoulder 36 formed ona latch lever 37. The latch lever 37 is urged in a clockwise directionby means of the spring 38. It is provided with an extension or foot 39at its lower end. The bell crank lever 34, 35 is provided with anupwardly projecting arm 40 which is connected to one end of a spring 41,such spring being anchored at its other end to the cover 3,'as showninFigure l. The bell crank lever is, therefore, urged in acounterclockwise direction. The bell crank lever 34, 35 is looselymounted.

on a rock shaft 42 journaled in any suitable manner in the cover 3 andprojecting outwardly from one side of the cover. The shaft is providedwith an external arm having a manipulating eyeleted arm 43 adapted toreceive a switch stick. Normally, this arm is housed in a downwardlyopening casing 44 carried by the cover 3 and may be reached by the hookend of a switch stick so that the arm may be pulled downwardly tomanually open the circuit interrupter or pushed upwardly to reset thecircuit interrupter. A lever or arm 45 is rigidly mounted on the rockshaft 42, see Figure l, and is connected by means of a spring 46 withthe arm 35 of the bell crank lever heretofore described.

The spring 46' holds a foot or extension 47 of the lever 45 inengagement with the under side of the arm 35 of the bell crank lever.The lever or arm 45 is provided with an extension 46 which, when therock arm or manipulating arm 43 is pulled downwardly, is adapted toengage the foot 39 of the latch lever 37 and move such latch lever tothe right as viewed in Figure l to disengage the pin 33 from theshoulder 36, and allows the springs 24 to raise the slide bar 22 andthus suddenly open the circuit interrupter.

On the other hand, provision has been made for the automatic opening ofthe circuit interrupter as by manipulating the extension 32 of the latch29 so thaton overload the latch 29 will be released and the toggle linkmechanism will be allowed to collapse temporarily, thus allowing thesprings 24 to suddenly open the switch. The toggle link will straightenitself out at the upper end of its stroke for it will be seen that theflattened face of the pin 33 will rock and will thus force the latch 37clear of the pin and allow the arm 34 of the bell crank lever to rockupwardly under the influence of the spring 41 and will thus againstraighten out the toggle link mechanism as up- When the circuitinterrupter is opened either by automatic or manual operation, the arm43, see Figure 2, rocks downwardly into a displayed position. Inresetting, the lineman engages the arm 43 with the switch stick andforces the arm upwardly, thus rocking the rock shaft 42 in a clockwisedirection. The arm or lever 45 rigid with such rock shaft engages theunder side of the lever 35 and forces the lever 35 upwardly, thusdepressing the arm 34 of the bell crank lever and moving the circuitinterrupter back into closed position. Obviously, at any time duringthis closing motion, the automatic means hereinafter described can tripthe latch 29 by engaging the extension 32in the event overload stillpersists.

The automatic means for tripping the circuit interrupter comprises asolenoid or magnet coil 48 wound about an insulating cylinder 49 whichmay be provided with end flanges, as shown, to provide a spool'likestructure for the reception of the winding. The cylinder 49 is continuedupwardly by means of a metal cylinder 50 whose lower edge is anchored inany suitable manner to the inner walls of the cylinder 49. The lowerends may be spun outwardly, as indicated in Figure l, to thus lock thecylinder 50 to the cylinder 49. The lower end of the cylinder 49 isclosed by means of an apertured plug 51 which constitutes a valve seatadapted to be normally closed by means of a downwardly biased valve 52.The valve 52 may be slotted at its upper end and may be guided by a pin53 which pin also limits the upward motion of the valve 52. The valve 52is made cylindrical and is seated in a deep cylindrical aperture so thatsmall vibrations of the plunger 55 will not cause it to open. Instead,considerable motion of the plunger 55 is required. This prevents pumpingof oil due to vibration of the plunger just before minimum value of tripcurrent is reached. it has been found that if no provision is made toprevent undue pumping of oil due to minute vibrations of the plunger,particularly as minimum value of trip current is approached, that theplunger will pump oil and cause tripping of the sectionalizer prior toits normal operation. However, by means of the construction hereinabovedescribed, this serious defect is avoided. There is, therefore, acoaction between the intake valve 52 and the pumping plunger since thesize of the pumping plunger and the length of its minute strokes justbefore the time minimum tripping current is reached, are so related tothe size and the length of the opening stroke of the intake valve thatthe intake valve remains closed and prevents pumping while the plungeris making its minute strokes hereinabove described. The plug 51continues upwardly and the upper end of the plug is slotted to lesseneddy currents.

It is preferable to form the plug 51 of magnetic material, whereas, thevalve 52 is preferably formed of nonmagnetic material. A magnetic yoke54 extends across the top and bottom and around the sides of the magnetcoil 48 and a reduced extension 52 of the plug 51 may be swaged orriveted in an aperture formed in the lower portion of the yoke 54. Theupper portion of the yoke 54 is apertured for the cylinder 53. Withinthe cylinder formed of the members 49 and 50 a magnetic plunger 55 ispositioned. Thisrplunger has an aperture extending through it which isnormally closed by a down wardly spring pressed ball valve 56.Preferably, the plunger 55 is slotted through a considerable portion ofitsextent to reduce eddy currents. The magnetic plunger 55 is urgedupwardly by means of a spring 57 seating against a shouldered portion onthe plunger and loosely surrounding a reduced portion thereof. The lowerend of the spring 57 rests on the upper part of the magnetic plug 51.The cylinder 50 carries a transverse pin 58 which limits the upperstroke of the plunger 55. This pin also limits the lowermost position ofthe counting pistension or reduced portion 60.

From the description thus far given, it is clear that the magneticplunger 55 constitutes a pumping piston and when an overload occurs theplunger 55 will be drawn downwardly through the action of the coil 48.Oil will flow upwardly past the check valve 56. When the current flowceases through the action of a repeating circuit interrupter hereinafterdescribed, the plunger 55 rises and pumps oil upwardly into the spacebetween the plunger or pumping piston 55 and the counting piston 59 andthus raises the counting piston 59. Successive actions of the plunger orpumping piston 55 will move the counting piston 59 upwardly in astep-by-step manner. The lower valve 52 is arranged to allow oil to passinto the space below the pumping piston 55 on the up stroke of suchpiston.

A tripping member 61 is pivoted as indicated at 62' and normallyoccupies the position shown in Figure 1. It is adapted to be rocked in aclockwise direction when the counting piston 59 arrives at apredetermined point. When the tripping member 61 is rocked to the right,its normal vertical arm 62 engages the extension 32 of the latch 29 andtrips the latch and allows the circuit interrupter to suddenly open aspreviously described. The tripping member 61 is provided with anadjustable screw 63 and a lock nut to lock the screw in its adjustedposition. The screw is threaded through the norrnal horizontal arm 64 ofthe tripping member and is adapted to be engaged by the extension 69 ofthe counting piston 59. Obviously, the number of strokes required beforetripping of the circuit interrupter occurs is determined by theadjustment of the screw 63.

It is to be understood that the electrical circuit extends through themagnet coil 48 to one of the stationary contacts 14 through the arms 16and the conductor 19 to the other stationary contact 14.

This circuit interrupter is intended to be used with a reclosing circuitinterrupter of any suitable type. As shown in the diagrammatic view ofFigure 4, the reclosing circuit interrupter is indicated by thereference character 65 and is placed between the supply transformer 66and the line 67. Branch lines 68 extend outwardly from the line 67 andcircuit interrupters of the type hereinabove described are placed in thebranch lines 68. These circuit interrupters are indicated by thereference charactor 69.

The operation of the system is as follows:

Assume that an overload occurs on one of the branch lines 68. Themagnetic plunger or pumping piston 55, see Figure l, of the circuitinterrupter 69 is drawn downwardly, as the magnet coil 45 thereof is theordinary series coil, and oil passes through it to a position below thecounting piston 59. The repeating circuit interrupter 65 in the mainline 67 opens and the load current ceases to flow through the magnetcoil &8 of the circuit interrupter 69. Consequently, the pumping pistonor plunger 55 rises and pumps oil upwardly beneath the counting piston59 and thus moves the counting piston 59 upwardly one step. The upwardmotion of the piston :5 occurs only when there is no current flowingthrough the magnet coil 43, and, consequently, when there is no currentiiowing through the contacts of the circuit breaker.

When the repeating circuit interrupter 65 closes, if the fault on thebranch line 6% under consideration has disappeared, the counting pistonwill reset itself as hereinafter described. However, if the faultpersists, the pumping action of the piston 59, see Figure l, is repeatedfor each reclosing of the reclosing circuit interrupter 65 and thecounting piston 59 moves upwardly in a step-by-step manner and trips thecircuit interrupter 69. The tripping of the circuit interrupter 69occurs when there is no current flowing through the circuit interrupter.Consequently, there is no arcing at the contacts and a much simplerconstruction can be employed. After the circuit interrupter 6% in theline on which the fault exists has opened, the reclosing circuitinterrupter 65 again closes and supplies power to the remaining branchlines, the defective branch line having been isolated from the system bythe operation of the circuit interrupter 69 on such line.

Figure 3 shows a lfurther form of construction whereby a different meansis provided for determining the adjustment for the counting piston; thatis to say, for determining the point at which the counting piston willtrip the circuit interrupter. Similar reference characters are employedas those used in Figure 1 wherever the parts are alike. The principaldifierence between the two constructions resides in the fact that thecounting piston 59' is provided with an adjustable screw 60 which may beadjusted upwardly or downwardly as required and which will determine thepoint at which it will engage the trip ping member indicated generallyat 61.

A further difference in the construction shown in Figure 3 from thatdescribed is that the magnetic plug 51' is provided with a reducedportion around which the indicated generally by the reference character72, is posi-- tioned. This valve structure is shown more clearly inFigure 6. It will be seen that it comprises a body portion 73 and anon-magnetic ball valve 74. The ball valve normally seats, 'as shown inFigure 6, and closely fits the cylindrical portion 75 and is locatedbelow the outlet ports or transverse openings 76. A slidable member 77is positioned above the valve and has an upper flange 78 located abovethe body portion 73. It has a limited amount of longitudinal motion andis held against re moval from the body portion 73 by means of a limitscrew 79 which is adapted to be engaged by the lower enlargement 89 ofthe member 77 when such member is drawn upwardly. The member 77 isnon-magnetic and when the magnetic pumping plunger 7%), see Figure 6, isin its lowermost position, at approximately minimum trip current, theupper flange 78 of the member 77 rests against the upper portion of thebody 73 and thus prevents the ball valve 74 from rising to a positionwhere it would establish communication between the inlet port 81 and theoutlet ports '76. This, it will be seen, prevents the valve fromexecuting opening motion until the magnetic pumping piston 76 movesupwardly upon cessation of overload current. At this time the member 77is free to move upwardly and the valve consequently is free to open andallow oil to be drawn into the lower end of the cylinder 32, see Figure5.

Immediately above the pumping piston, an impulse valve assembly ispositioned. This valve assembly is positioned within and is secured tothe cylinder and forms a partition between the pumping piston 79 and thecounting piston 83. The impulse valve assembly cornprises a body portionor partition proper 84 which is apertured as indicated at 85 and whichis provided with a valve disk 86 on its lower side, spring presseddownwardly by means of the spring 87. The valve disk 86 is free to moveupwardly when the pumping plunger 70 suddenly moves downwardly onoverload and tends to project a jet of oil upwardly past its check valve83. This protects the counting piston 83 from the jet of oil.

It will be seen from the structure described immediately above that themagnetic pumping piston 70 is drawn downwardly on overload against theaction of the spring 71. Upon cessation of overload current, ashereinbefore described, the magnetic plunger is released and the spring71 pushes it upwardly and causes it to pump oil beneath the countingpiston 83 and thus raise the counting piston a predetermined amount. Thenumber of strokes rcquired to cause tripping of the .sectionalizer isdetermined by the adjustment of the pin 89 carried by the trip lever 90.This pin is provided with a plurality of apertures through any one ofwhich the pin 91 may be passed to thus secure it to the trip lever 90 ina selected adjusted position.

In the first forms of the invention, a slow leak is provided around thecounting piston 59 or 59', see Figures 1 and 3, so that the countingpiston slowly settles downwardly to its initial position. In theconstruction shown in Figure 5 a slow leak is provided around thecounting piston 83. This leak is secured by the clearance between thecounting pistons and their respective cylinders and is too small to showin the drawings. If a number of strokes of the pumping piston hasoccurred, less than that required to trip the circuit interrupter, andif the fault is thereafter cleared, it is apparent that the countingpiston will settle downwardly, in all forms of the invention, to itsinitial position and will be ready for operation from its initialposition for any subsequent fault or faults that may occur.

On the other hand, if the circuit interrupter has been tripped by acontinuing fault with a predetermined number of operations of thepumping piston, thereafter the counting piston will slowly settle downto its initial position so that no thought is required on the part ofthe operator when he resets the circuit interrupter.

No claim is made to the specific details of the structure shown inFigures 6, 7, and 8.

It is to be noted that this invention provides a circuit interrupterwhich opens the circuit only when there is no current flowing. Thepumping action takes place only when there is no current flowing.Consequently, the last pumping action which causes the counting pistonto move to tripping position occurs when there is no current flowing.

Another feature which is to be noted is that there is no sudden violentshock to the counting piston. It is not driven upwardly when there is anoverload. The only sudden shock of any part of the apparatus onoverload, while the current is flowing, is that imparted to the pumpingpiston. This causes no damage whatsoever and no jar to the mechanism asthe pumping piston is merely suddenly drawn downwardly without any shockbeing imparted to any part of the apparatus.

Although this invention has been described in considerable detail, it isto be understood that such description is intended as illustrativerather than limiting, as the invention may be variously embodied and isto be interpreted as claimed.

We claim:

1. In an oil immersed electric circuit sectionalizer includiing normallyclosed contact means, actuating means for opening said contact means,and releasable locking means normally holding said actuating meansinactive, the combination with a trip element for releasing said lockingmeans, of. an overload responsive assembly immersed in said oil andcomprising a cylinder, a coil surrounding the cylinder, said cylinderbeing open at one end and closed at the other end by a closure memberincluding a check valve movable a predetermined distance for admittingoil into said cylinder, a magnetic plunger in said cylinder movabletoward said closure member in response to a predetermined overloadcurrent flow in said coil, a spring in said cylinder disposed betweensaid closure member and magnetic plunger and urging said plunger fromsaid closure member, said plunger having an axially disposed portextending therethrough and a check valve closing said port when saidplunger moves from said closure member, movement of said plunger fromsaid closure member also causing a predetermined movement of said checkvalve and drawing oil into said cylinder, means limiting the extent ofmovement of said plunger under the influence of said spring, the openend of said cylinder extending from said coil, a counting piston in saidcylinder movable toward said trip element for operating said tripelement, said plunger being disposed between said closure member andcounting piston, said piston being arranged to release said lockingmeans and being moved toward said trip element only on cessation ofoverload current, said valves permitting flow of oil through saidcylinder only in the direction of said counting piston and only oncessation of overload, and adjustable means for determining the numberof operations before tripping occurs.

2. In an alternating current circuit interrupter, normally closedcontact means, normally ineffective opening means for opening saidcontact means, a coil energized by alternating current, a coil spoolconstituting a cylinder, an armature and plunger normally occupying aninitial position and coacting with said coil spool and constituting apumping plunger arranged to be drawn into said coil spool uponenergization of said coil by overload current, means urging said plungerto execute a return stroke to its initial position, hydraulic countingmeans against which fluid is pumped by said plunger to move saidhydraulic counting means in a step-by-step manner, said hydrauliccounting means being arranged to render said opening means effective toopen said contact means when said counting means arrives at apredetermined position, outlet valve means between said plunger and saidhydraulic counting means and arranged to close on return stroke of saidplunger, and intake valve means including a stationary member and acoacting movable member, said stationary member having an elongatedpassage therethrough and coacting with said movable member to maintain aseal between said stationary member and said movable member while saidmovable member executes an opening movement and moves along saidpassage, said movable member at the extreme limit of its openingmovement allowing flow of oil through said passage, whereby pumpingaction of said piston due to vibrations from the cyclic variation of thealternating current is prevented and pumping action of said piston uponcessation of overload current is allowed.

3. An oil immersed alternating current tripping device comprising anoverload responsive assembly having a cylinder, a coil surrounding thecylinder, said cylinder being open at one end and closed at the otherend by a closure member including a check valve for admitting oil intosaid cylinder, said check valve including a valve seat and a movablemember coacting with said valve seat, said valve seat being elongatedand maintaining a seal with said movable member while said movablemember moves through a predetermined distance with reference to saidvalve seat, a magnetic plunger in said cylinder movable toward saidclosure member in response to an alternating current flow in said coilof a predetermined value, a spring in said cylinder disposed betweensaid closure member and magnetic plunger and urging said plunger fromsaid closure member, said plunger having an axially disposed portextending therethrough and a check valve closing said port when saidplunger moves from said closure member, means limiting the extent ofmovement of said plunger under the influence of said spring, the openend of said cylinder extending from said coil, and a counting piston insaid cylinder, said plunger being disposed between said closure memberand counting piston, said counting piston being advanced to operate as atripping means only on cessation of current of said predetermined value,said valves permitting flow of oil through said cylinder only in thedirection to advance said counting piston and only on cessation ofalternating current of said predetermined value.

4. An alternating current tripping device adapted to be immersed in oilcomprising a cylinder having a closed end, an inlet valve at the closedend of said cylinder, said inlet valve including two members one ofwhich is stationary and provided with a passage therethrough and theother of which is movable and coacts with said passage, at least one ofsaid members being elongated and maintaining a seal with the other ofsaid members While relative movement between said members is takingplace for a predetermined length of movement, a magnetic pumping plungerhaving a passage therethrough, a spring normally holding said plunger inan initial position spaced from said closed end, a coil surrounding saidcylinder for drawing said magnetic plunger inwardly against said springwhen energized by an alternating electric current of a predeterminedvalue, an outlet valve carried by said magnetic plunger and opening toallow oil to pass through the passage in said magnetic plunger when saidmagnetic plunger is drawn towards the closed end of said cylinder andclosing when said magnetic plunger is moved by said spring towards theother end of said cylinder, and a counting piston located in saidcylinder and positioned between said magnetic pumping plunger and saidother end of said cylinder and advanced in a step-by-step manner uponeach pumping stroke of said magnetic pumping plunger.

References Cited in the file of this patent UNITED STATES PATENTS1,737,649 Edsall Dec. 3, 1929 1,742,837 Wallace Jan. 7, 1930 1,805,082Edsall May 12, 1931 1,982,986 Garlington Dec. 4, 1934 2,029,780 Mazer eta1. Feb. 4, 1936 2,452,233 Gerard et al. Oct. 26, 1948 2,515,530Schindler July 18, 1950

